Obligations Surrounding Buying Someone a Drink

St. Patrick's Day is a big get out and party holiday. So, what are the obligations surrounding buying someone that you may be interested in a drink?

Is there an obligation to hang around and talk with the individual who purchased the drink for you? Some have said that you are not "obligated" to talk to the person, but if you don't you look like a terrible person; which to me means you are obligated.

If you are not a single person, do you instantly say you are not on the market and refuse the drink? But then what if the person buying said drink was only trying to talk and have a platonic relationship? Is that possible? I have been told that the person accepting the drink does not have to say they are taken right away, but it needs to come up in conversation - which leads back to question one, and also makes me wonder if the person who accepted the drink now looks shady because they accepted the free drink and they do not have an intention of furthering the relationship.

Now, if the person declines the drink, that makes them look as if they are a prude and rude.

IS THERE NO WINNING SITUATION HERE?! What is the RIGHT ANSWER!?